The present invention is directed to a sensing device. More particularly, the present invention pertains to a sensing device used to detect the presence or absence of liquid within a tube.
Fluid or liquid within a tube or conduit may be detected using ultrasonic waves. Typically, a transmitting transducer is positioned on one side of a tube and a receiving transducer is positioned on the opposing side of the tube. The transmitting transducer emits an ultrasonic signal, which is propagated through the tube wall and into the tube itself. If the tube is empty, no signal is received by receiving transducer. If there is liquid present in the tube, however, the receiving transducer receives a signal and conveys the signal to, for example, a control circuit.
Typically, the ultrasonic energy is generated and received by a pre-made joint sensor system consisting of a transmitting transducer and receiving transducer pre-fastened to a hollow, open-ended sleeve. In order to use the joint sensor system with a desired tube, a section of the tube is removed and the joint sensor system is joined to the tube at the area where the portion of tube has been removed. The tube is connected to the sleeve such that liquid passes through the sleeve, and the joint is then sealed at each end of the sleeve to the tube. The joint sensor system then becomes an integral part of the tube. While effective, such joints and seals are prone to leakage. In addition, placing the sensor integrally within the line of the tube is not only time-consuming, but also expensive.
In another embodiment, transducers are applied directly to the tube sidewalls with fastening agents such as screws or chemical means, such as adhesive. Unfortunately, these fastening agents do not always maintain a secure connection and may absorb and/or distort the ultrasonic waves. In addition, in this configuration, the bottom electrode of the transducer may not be in electrical communication with the control circuit effectively, and thus, the signal becomes distorted and/or attenuated.
Accordingly, there is a need for an ultrasonic liquid sensing device that maintains contact with the tube and does not distort or otherwise interfere with the transmission and reception of ultrasonic waves. Such a sensor is easy to mount and can be used and re-used with a variety of different sized and shaped tubes. Most desirably, no cutting of the tube is necessary and the tube maintains its structural integrity.